Max Planck Institute for Astronomy - Annual Report 2007

88 III. Selected Research Areas
III.4 Starburst Clusters in the Milky Way
The majority of stars are born not in isolation, but in
stellar clusters and associations. Interacting galaxies
like the Antennae galaxies are the birthplaces of massive
stellar clusters with several 100,000 to millions of
stars. Over time, these super star clusters are expected
to evolve into globular clusters quite similar to the
150 or so that constitute the Milky Way globular cluster
system, which formed about 13 billion years ago.
Among the most extreme star formation environments
in the present-day Milky Way are starburst clusters
with several 10,000 to 100,000 stars. As the stellar population
in starburst clusters contains stars with masses
from 0.1 to 120 solar masses, starburst clusters are
ideal testbeds to study star formation and early stellar
evolution across the entire range of stellar masses.
Fig. III.4.1. Location of the presently known starburst clusters
plotted on a map (courtesy of Wikipedia) of the Milky Way
spiral arm structure. The Sun's orbit is indicated by a black
circle, and the present-day position of the Sun by a yellow
dot. The small inserts show near-infrared observations of the
individual starburst clusters.
Local Spur
Perseus
WD2
Sagittarius
WD1
NGC3603
Starburst clusters with ages of a few million years represent
unique astrophysical laboratories, because they contain,
in a rather homogeneous environment, stars across
the entire stellar mass range from the upper mass cut-off in
the mass function down to the hydrogen burning limit (and
possibly beyond) and with the same metallicity and age.
As such, starburst clusters are the ideal places to study
star formation and to test theories on formation and evolution
of stars and clusters. Unlike interacting galaxies
such as the Antennae galaxies, where hundreds of super
star clusters have been identified, the Milky Way houses
only a handful of starburst clusters. Starburst clusters in
the Antennae, however, are barely resolved, restricting
study to the integrated properties of hundred thousands
of stars. In the Milky Way, on the other hand, starburst
clusters can be resolved into thousands to tens of thousands
of stars, and the properties of each star can be derived
individually.
Galactic Starburst Clusters
Milky Way starburst clusters can be found either in the
galactic center region or in spiral arms. Because of strong
RSGC1
Arches
Galactic
Center
Quintuplet
Norma
Scutum-Crux
Sun’s Orbit
Obscured